Chain tightener



FIG. 1 is a front, top and side perspective view of the chain tightener showing my new design;

FIG. 2 is an end elevational view thereof, the end opposite being a mirror image of the end shown in FIG. 2;

FIG. 3 is a side elevational view thereof, the side opposite being a mirror image of the side shown in FIG. 3;

FIG. 4 is a top plan view thereof; and,

FIG. 5 is a bottom plan view thereof. 

The ornamental design for a chain tightener, as shown and described. 